fix: gpt-oss streaming dropping normal content when tools are provided but not used (#9657)

python/sglang/srt/function_call/gpt_oss_detector.py

@@ -81,6 +81,29 @@ class GptOssDetector(BaseFormatDetector):
         # Always use HarmonyParser for parsing to ensure proper filtering
         events = self.harmony_parser.parse(new_text)
 
+        # If there are no parsed events and the chunk contains no Harmony structural
+        # markers, treat it as plain text and pass it through. This fixes a bug where
+        # normal content was held in the buffer when tools were provided but not used.
+        if not events:
+            has_harmony_markers = any(
+                marker in self._buffer
+                for marker in (
+                    "<|start|>",
+                    "<|channel|>",
+                    "<|message|>",
+                    "<|constrain|>",
+                    "<|end|>",
+                    "<|call|>",
+                    "<|return|>",
+                    "assistantfinal",
+                )
+            )
+            if not has_harmony_markers:
+                # Plain text with no tool markers — emit as normal content
+                out = self._buffer
+                self._buffer = ""
+                return StreamingParseResult(normal_text=out, calls=[])
+
         # Quick check if we might have tool calls
         if (
             "<|channel|>commentary to=" not in self._buffer